Measuring and test equipment currently employed by telephone service providers customarily contain a variety of conditioning and signal generation capabilities, which enable service and maintenance personnel to apply a prescribed number of electrical stimuli to a line (a subscriber loop), for the purpose of trouble-shooting the line and measuring its performance.
A relatively simplified non-limiting block diagram of a telephone network containing such equipment is shown in FIG. 1 as comprising a distribution of a plurality of (microprocessor-controlled) remote measurement units (RMUs) 11, which are installed at a plurality of sites geographically remote with respect to each other and a supervisory site 12.
An RMU 11 includes various components, such as analog-to-digital converter (ADC) and digital-to-analog (DAC) converter units, and tone generation and electrical conditioning circuitry which, under the control of a firmware-resident measurement and test mechanism employed by an on-board processor (microcontroller), selectively transmit prescribed test signals to the line, and may also condition the telephone line with electrical circuit parameters, that allow an associated line measurement unit to conduct line measurements and thereby determine the current state of the line and its ability to successfully perform as intended.
For this purpose, each RMU 11 is typically of the type that conforms to computer interface requirements defined in Issue 3 of AT&T Publication KS-23253, and contains internal firmware which is operative to perform various test operations on network lines 13 and (subscriber) termination equipment 15, under the control of one or more host computers, video display terminals (VDTs) or data terminal units (DTUs) 21 at a supervisory site 12, which have the capability of accessing the remote test equipment 11 through attendant modem devices 23 and 24, such as industry standard Hayes `AT`-compatible 300/1200 units, that are linked to a central office 25.
In order to ensure that the test device installed at the remote site is functioning properly, it is customary practice to monitor the performance capability or `health` of the device by occasionally taking it off-line, and performing test diagnostics on its own internal components. Unfortunately, the manner in which the performance capability of such test devices has been monitored in the past does not readily provide the system user with a significant amount of useful diagnostic information in the event of an anomaly.
More particularly, it is customary practice to examine operational capability of such equipment, either on a very infrequent basis (e.g. every six months to a year), or in the event of a manifest (e.g. catastrophic) failure. Otherwise, it is simply assumed that the device is operating correctly and is expected to continue to do so. Because such `health` evaluation procedures do not track malfunction history of the device in a manner that provides a statistically meaningful indication of its performance, there is no way of knowing whether or not the device is likely to incur a degradation of performance or what possible or probable failure may take place.